CHRNB2 and Norrie disease: The GEE-GMDR method detected the most significant tetragenic interaction model (rs2072660- rs1209068- rs11030134- rs6011770) with an empirical p value of 2.62e-04 and test accuracy of 0.5780, supporting our hypothesis of a possible interaction among CHRNB2, NTRK2, BDNF, and CHRNA4 underlying ND (Table 3).